The polymerization of 1,3-butadiene to form high cis-1,4-polybutadiene employing organonickel based catalyst systems has been described in several patents and publications.
In U.S. Pat. No. 3,856,764, issued Dec. 24, 1974, there is disclosed a process for producing cis-1,4-polybutadiene by contacting 1,3-butadiene with a catalyst consisting of (1) at least one organoaluminum compound, (2) at least one nickel compound selected from a class consisting of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel tetracarbonyl and (3) at least one hydrogen fluoride complex prepared by complexing hydrogen fluoride with one or more members of a class consisting of ketones, esters, ethers, alcohols, nitrites and water.
In U.S. Pat. No. 3,528,957, issued Sep. 15, 1970, there is described the solution polymerization of butadiene to form high cis polybutadiene which comprises polymerizing butadiene in the presence of an organometal compound of groups 1, 2, and 3 of the Periodic Table with particular emphasis to trialkyl aluminum compounds and (2) at least one compound from the class consisting of organonickel compounds, and (3) at least one boron trifluoride complex prepared by complexing boron trifluoride with a member of the class consisting of monohydric alcohols, phenols, water and mineral acids containing oxygen.
In U.S. Pat. No. 3,910,869 issued Oct. 7, 1975, there is disclosed a process for the polymerization of butadiene to form polymers containing a high proportion of the butadiene units in the cis-1,4 configuration which comprises contacting the butadiene under solution polymerization conditions with a catalyst comprising (1) an organoaluminum compound, (2) an organonickel compound and (3) hydrogen fluoride.
In U.S. Pat. No. 3,483,177, issued Dec. 9, 1969, there is disclosed a process for the polymerization of butadiene to form polybutadiene containing a high proportion of the butadiene units in the cis-1,4 configuration which comprises contacting butadiene under polymerization conditions with a catalyst comprising (1) at least one organometallic compound in which the metal is selected from Groups I, II, and III of the Periodic System; (2) at least one organometallic compound selected from the class of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel carbonyl; and (3) at least one boron trifluoride complex prepared by complexing boron trifluoride with a member of the class consisting of ketones, aldehydes, esters and nitrites.
In U.S. Pat. No. 4,020,255, issued Apr. 26, 1977, there is disclosed a process for preparing high cis-1,4-polybutadiene which comprises continuously polymerizing butadiene in an inert aliphatic or cycloaliphatic solvent using as a catalyst a mixture comprising (a) at least one trialkylaluminum wherein the alkyl group contains from 2 to 8 carbon atoms; (b) at least one nickel salt of a carboxylic acid; and (c) at least one boron trifluoride complex of ethers in which each of the individual catalyst components are continuously injected into the polymerization vessel containing the mixture of butadiene and inert solvent.
The second most important industrial catalyst system based on nickel to catalyze polybutadiene is the system employing a nickel carboxylate in conjunction with an organoaluminum compound and boron trifluoride etherate. This system also yields extremely high cis-1,4-polybutadiene. However, the molecular weights are slightly lower than the system employing the hydrogen fluoride or hydrogen fluoride complexes.
In many applications of cis-1,4-polybutadiene, it is usually desirable to employ higher molecular weight polymers than those generally obtained from either one of the immediately aforementioned polymerization systems. For example, in certain tire applications it is desirable to use a high cis-1,4-polybutadiene having a DSV (dilute solution viscosity) of about 3 or higher.
The invention described herein deals with the use of various alkali or alkaline earth metal salts of organic carboxylic acids, such as calcium carboxylate compounds, as molecular weight regulators for the above-mentioned polybutadiene syntheses. The utilization of these molecular weight regulators in organoaluminum/organonickel/fluorine catalyzed 1,3 -butadiene polymerization systems permits the synthesis of high molecular weight cis-1,4-polybutadiene elastomers without significantly reducing the monomer conversion rate of the polymerization process.
These syntheses of various molecular weight polybutadienes can readily be effected in an anionic or an emulsion polymerization system by the mechanism of the catalyst level or the chain transfer level, respectively. However, these polymerization systems do not yield high cis-1,4-structure typical of the aluminumn/nickel/fluorine-based solution polymerizations mentioned above. For example, a typical alkyllithium initiated (anionic) 1,3-butadiene polymerization generally yields polymers containing 36-44 weight percent cis-1,4 polymer, 48-50 percent trans-1,4 polymer and 8-10 percent, 1,2 structures. On the other hand, a typical emulsion polymerization of butadiene yields a polymer containing about 60 percent trans-1,4 structure, about 20 percent cis-1,4 structure, and about 20 percent 1,2 structure.
The present invention expands the scope of high cis-1,4 directing 1,3 -butadiene polymerization systems by producing high molecular weight cis-1,4-polybutadiene while maintaining desirable polymerization conversion rates.